1. Field of the Invention
The present invention relates to a turner bar for a web-fed rotary printing machine.
2. Description of the Related Art
In web-fed rotary printing machines, printed material webs of one-quarter or one-half width must be offset laterally by their width or by a specific amount. The offset is achieved by the printed material web being wrapped around two turner bars by 180.degree. in each case. In this arrangement, the two turner bars may be parallel or crossed at 90.degree., depending on the turning desired. While the printed material web is wrapping around these turner bars, sliding friction occurs because of the contact with the stationary turner bar. This friction influences the web tension. When ink which has not been fully dried is on the printed material web, the turner bar can cause set-off and smearing of the printed image. For these reasons, prior art turner bars circulate air around the turner bars.
A prior art turner bar of this type, to which blown air is applied, is disclosed by DE 32 15 472 C2. Pressurized air is directed to the turner bars through lines. Through specifically arranged radial holes, the air passes out of the turner bar where the moving printed material web wraps around the latter. As a result, the web floats over the turner bar with considerably reduced friction "without contact", on a moving and thus non-uniform air cushion.
Depending on the tension of the printed material web, the pressure of the air fed and the randomly more or less uniform distribution of the moving air cushion, the printed material web floats around the turner bar on a larger or smaller radius. As a result, the register offset and the axial offset of the printed web become larger or smaller. That is to say, the position of the printed material web with respect to the turning bar does not remain constant but rather runs axially, i.e., in the longitudinal direction of the turner bar, and in the circumferential direction of the turner bar.
A further disadvantage of the known turner bar to which pressurized air is applied is that paper fibers which are torn out of the printed material web in the longitudinal direction when the web is being slit, and to some extent continue to adhere to the web edge, are entrained at the turner bar by the blown air and are distributed over the entire area by the air stream. Furthermore, a constant expenditure of energy is necessary for each turner bar in order to generate the blown air. The hose runs for the compressed air are complicated, in particular if it is intended to change positions of the turner bars. If the positions of the turner bars are changed, the hose run must be carried along automatically with the turner bar, and it is necessary to compensate for different hose lengths for each position of the turner bar. A further disadvantage of using the blown air is that during the compression of the air, and during the emergence of the compressed air from the holes of the turner bars, clearly audible noise is produced.